As mobile devices have been increasingly developed and the demand for such mobile devices has increased, the demand for secondary batteries as an energy source has also sharply increased.
Depending upon kinds of external devices in which such secondary batteries are used, the secondary batteries may be used in the form of a single battery or in the form of a battery pack having a plurality of unit cells electrically connected to each other. For example, small-sized devices, such as a mobile phone, can be operated for a predetermined period of time with the output and capacity of one battery. On the other hand, a battery pack needs to be used in middle or large-sized devices, such as a laptop computer, a portable digital versatile disc (DVD) player, a small-sized personal computer (PC), an electric vehicle, and a hybrid electric vehicle, because high output and large capacity are necessary for such middle or large-sized devices.
Among secondary batteries, a lithium secondary battery is widely used since the lithium secondary battery has high output and large capacity.
However, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to overcharge of the lithium secondary battery, overcurrent in the lithium secondary battery, or other external physical impact applied to the lithium secondary battery. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as overcharge of the lithium secondary battery or overcurrent in the lithium secondary battery, are loaded on a battery cell in a state in which the safety elements are connected to the battery cell.
Generally, the PCM is electrically connected to the battery cell via conductive nickel plates by welding or soldering. That is, nickel plates are connected to electrode tabs of the PCM by welding or soldering, and the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. To this end, a plurality of parts is necessary, which complicates an assembly process of the battery pack. In addition, a space necessary to receive the battery cell is reduced.
Consequently, there is a high necessity for a battery pack, a structure of which is optimized such that the number of members mounted at the top of a battery cell is reduced even in a state in which a conventional battery cell is used and a conventional assembly method is maximally utilized, whereby stable coupling among the members mounted at the top of the battery cell is achieved and, in addition, the capacity of the battery cell is increased.
Meanwhile, there is an increasing necessity for a wireless charging type battery pack that is capable of solving problems or defects of a wired charging type battery pack. In such a wireless charging type battery pack, the battery pack is charged through electromagnetic induction based on current/electromagnetic interaction generated between two opposite metal coils.
In order to achieve electromagnetic induction, it is necessary to further install a charging coil at the battery pack. However, installation of the charging coil is very difficult due to a limited space of the battery pack. That is, installation of the charging coil leads to the increase in size of the battery pack. In addition, a process of assembling the battery pack is complicated. Furthermore, the charging coil may interfere with the PCM.
Therefore, there is a high necessity for a battery pack which can be wirelessly charged through electromagnetic induction and can be easily assembled while the increase in size of the battery pack is restrained without occurrence of any interference phenomenon.